Intro To Solvent Welding Plastic

I've been compiling a list mainly for personal use of common engineering plastics used in Nerf and their solubility in the common solvents and figured I'd share what I have since I know a lot of you *cough*Bob*cough*BadWrench*cough* will have some more to add.

Solvent-welding plastic involves using a solvent to partially liquefy plastic along the joint and allowing the joint to solidify causing a permanent chemical weld. It is similar in end result to heat welding metal or thermoplastic. Welded joints have an advantage over other adhesives in that there is no third material creating the joint. Joints are also airtight when created properly. Thus, for example, PVC/ABS cement is my preferred method for attaching vinyl tubing (flexible PVC) to air tanks (made from ABS) when simply connecting existing tubing is not possible or practical.

The process of solvent welding is simple. Apply solvent to the pieces you want to adhere, push the pieces together (not necessarily in that order), and then wait for the solvent (they are all very volatile) to evaporate into the environment and the polymer strands of the plastic to solidify. The most difficult part is thus finding solvents that will dissolve the plastic in question.

Safety Warning: most of these solvents are toxic. Do not inhale them, especially deliberately. Use in a very well ventilated area. They are also highly volatile and thus flammable. Keep away from open flames. Do not smoke while applying solvents.

On solubility

The following is an incomplete list of the most common plastics used in Nerf and their compatibility with common solvents. A "Y" indicates that the solvent will dissolve the plastic in question. A "N" indicates that the solvent is not recommended for use with that plastic. Either it does not dissolve the plastic at all or does so poorly.

Dichloromethane: Also known as Methylene chloride. Found primarily in paint stripper. Used as an industrial solvent. Banned in Europe.

Methyl ethyl ketone (MEK): Also known as Butanone. A large component of almost all plastic cements especially ABS and polystyrene cement. Can be bought pure.

Methyl benzene: Also known as Toluene. Used mostly as a paint thinner or paint remover. Found along with MEK in polystyrene model kit cement.

Tetrahydrofuran: Found almost exclusively in PVC cement. Can also be in some varnishes.

Plastic cement is generally comprised of a solvent (or mixture of solvents) along with dissolve plastic resin of the plastic in question. Thus PVC cement will contain dissolved PVC along with the solvents.
Examples:
Genova ABS cement is around 20% Acetone, 60% MEK, and 20% ABS resin.
Oatey Green Transition cement is around 40% Tetrahydrofuran, 35% Acetone and MEK, 10% Cyclohexanone, and 15% PVC resin.
Look either on the can or search for Material Safety Data Sheets for the ingredients and quantities, and then look up which plastics these will work with.

This post has been edited by Zorn's Lemma: 21 April 2010 - 07:17 PM

"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
Kruger and Dunning (1999)

not quite. the amount of acetone in nail polish remover is only enough to soften a very thin layer of acrylic paint. it is not in high enough concentration to fuse plastics. however it does work well to clean plastics as prep for painting.

zorn great writeup. ive tried to use straght acetone and found that its a tad rough to work with. i like the premix that taps plastics sells called weldon 3. the liquid stuff not the gel (weldon 16). tho the gel has its uses too.

Forgive my spelling and grammar. I post from my cell phone a lot. Sometimes when I'm on the can at work.

Would nail polish remover seal a BBBB tank sufficiently so that it does not blow up? I would like to know this since had a... let's say... educational experience (I cut the tank in half to fix the check valve)(I was an idiot back then).

-gmzamz

This post has been edited by gmzamz: 05 January 2010 - 01:43 PM

96% of all Statistics are made up. If you are one of the 5% of people that suck at making up statisitics, post this in your signature.

Would nail polish remover seal a BBBB tank sufficiently so that it does not blow up? I would like to know this since had a... let's say... educational experience (I cut the tank in half to fix the check valve)(I was an idiot back then).

You misunderstand. These chemicals are solvents not adhesives. They will allow two plastic pieces to be bonded together, but the solvent itself just dissolves the plastic. It would actually weaken a pressure tank to simply apply the solvent to it. You could probably use PVC or ABS pipe weld on the seam, though. They actually contain some dissolved pvc and can actually add mass to the joint.

Another note: 100% acetone is available cheaply in the health and beauty section of most department stores. Makes sure that it SAYS 100%, though. MEK is substantially better at dissolving the same plastics that acetone does, though you'll probably find that PVC pipe weld contains both. Probably for a good reason which I don't really know.

Nice idea. I don't know how easy it's going to be to fill out such a table, though.

My solvent of choice that's currently available to me is MEK. It's next to the paint thinner on the shelves of my local hardware stores. Although, if I could locate a source for ethylene dichloride, the results I obtained with it (back in the 70s) were often superior. I think the distribution of EDC is probably pretty limited these days. Chloroform is another solvent that can bond a variety of plastics, and might still be obtainable from some drug stores. Some off-the-shelf cements (e.g. Plastruct Liquid Weld) consist primarily of blends of MEK and Chloroform. Blends can sometimes weld dissimilar plastics which don't actually have a single-chemical solvent in common.

Most of these solvents are thinner than water itself, but almost all can be made into thicker preparations by dissolving solids into them. I have thickened MEK with styrene, with ABS scraps, or with cellophane, to make cements that will hold their place. What you thicken it with will affect how it works.

With a few combinations, like acrylic to acrylic using MEK, it's actually possible (though not easy) to get an invisible seamless joint in transparent material.

As has already been mentioned, these solvents mostly work by diffusing out of the joined plastics and into the air, and many are dangerous if inhaled - some even carcinogenic. If you can smell it ... that really can't be good.

Oh, and one more thing -- almost all of these solvents are highly flammable, and in most cases if you even smell the smoke of combustion, just f'ing CALL 911 NOW! The fumes from burning some of exactly these kinds of solvents were used as POISON GAS in the first world war.

This post has been edited by Just Some Bob: 05 January 2010 - 02:14 PM

Would nail polish remover seal a BBBB tank sufficiently so that it does not blow up? I would like to know this since had a... let's say... educational experience (I cut the tank in half to fix the check valve)(I was an idiot back then).

You misunderstand. These chemicals are solvents not adhesives. They will allow two plastic pieces to be bonded together, but the solvent itself just dissolves the plastic. It would actually weaken a pressure tank to simply apply the solvent to it.

Another note: 100% acetone is available cheaply in the health and beauty section of most department stores. Makes sure that it SAYS 100%, though. MEK is substantially better at dissolving the same plastics that acetone does, though you'll probably find that PVC pipe weld contains both. Probably for a good reason which I don't really know.

Okay, thanks. Oh well...

-gmzamz

96% of all Statistics are made up. If you are one of the 5% of people that suck at making up statisitics, post this in your signature.

Would nail polish remover seal a BBBB tank sufficiently so that it does not blow up? I would like to know this since had a... let's say... educational experience (I cut the tank in half to fix the check valve)(I was an idiot back then).

You misunderstand. These chemicals are solvents not adhesives. They will allow two plastic pieces to be bonded together, but the solvent itself just dissolves the plastic. It would actually weaken a pressure tank to simply apply the solvent to it.

Okay, thanks. Oh well...

-gmzamz

As I understand it, you cut your tank in half. You can weld it back together, but nail polish remover is not going to cut it. I suggest ABS cement since it will give you the most effective bond for the amount of effort required in finding it and using it and not getting yourself killing.

I've updated the OP with 1,2 Dichloroethane per Bob's suggestion, as well as Tetrahydrofuran and Cyclohexanone, which are both common components in PVC cement and paint thinners.

Most of these solvents will be found as components of pipe (ABS or PVC) and plastic kit (Polystyrene) cement and/or paint thinners and strippers.

Also, "N" on the chart does not necessarily mean the solvent will not work with the plastic at all, but that it is not recommended on basis of strength. For example, UHMW polyethylene will be degraded by chlorinated hydrocarbons (Ethylene dichloride and Methylene chloride), but no where near as effectively as Toluene.

"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
Kruger and Dunning (1999)

It's nice to know that acetone can be of use if I ever need to create a weld between two guns.

Doing this as I speak. I have no idea when I got it...my DAD got it some 15 years ago, but that doesn't matter. Anyways, it keeps jerking around all over the place. I try to hold it with a rag...It doesn't look like...much.

After allowing one day to cure, telescoping sizes of vinyl tubing could be pulled apart with a bit of force and without any tearing (in other words, no chemical bonding between the two sizes of tubing). Did I not wait long enough or is this just the wrong stuff? Should I have gotten the transition cement? (I would have, but they only had one size and it was waaaay to big). Based on Zorn's chart, it appears that this should work on the tubing (as I think the tubing I used was flexible PVC).

Sometimes vinyl is just vinyl.
...actually, probably most of the time.

PVC is a member of the vinyl group, but highly specialized, as are the solvents for it.

Plain vinyl, as used in most flexible tubing and lots of upholstery, is actually quite difficult to solvent weld with any mechanical strength. Better to just use mechanical couplers. If you're trying to build things like checkvalves out of telescoping sizes, vinyl is probably not the right stuff to start with.

Oh, and that stuff in your picture is transition cement. You can know this because it lists PVC, CPVC and ABS. Some other cement that actually said "transition" on the can probably would not have done any better anyway.

Sometimes vinyl is just vinyl.
...actually, probably most of the time.

PVC is a member of the vinyl group, but highly specialized, as are the solvents for it.

Plain vinyl, as used in most flexible tubing and lots of upholstery, is actually quite difficult to solvent weld with any mechanical strength. Better to just use mechanical couplers. If you're trying to build things like checkvalves out of telescoping sizes, vinyl is probably not the right stuff to start with.

Oh, and that stuff in your picture is transition cement. You can know this because it lists PVC, CPVC and ABS. Some other cement that actually said "transition" on the can probably would not have done any better anyway.

Okay, thanks for the info. I also posted because I had a joint break after waiting 2 hours (which for is for some reason the advertised cure time) that was between Nerf ABS plastic and CPVC. I'm guessing the problem there was me waiting two hours. Thanks for clearing that up, Bob!